class Containers::PriorityQueue

  1. lib/containers/priority_queue.rb
Parent: Containers

A Priority Queue is a data structure that behaves like a queue except that elements have an associated priority. The next and pop methods return the item with the next highest priority.

Priority Queues are often used in graph problems, such as Dijkstra’s Algorithm for shortest path, and the A* search algorithm for shortest path.

This container is implemented using the Fibonacci heap included in the Collections library.

Methods

Public Class

  1. new

Public Instance

  1. clear
  2. delete
  3. empty?
  4. has_priority?
  5. next
  6. pop
  7. push
  8. size

Included modules

  1. Enumerable

Public Instance Aliases

length -> size
next! -> pop

Public Class methods

new (&block)

Create a new, empty PriorityQueue

[show source] 
# File lib/containers/priority_queue.rb, line 16
def initialize(&block)
  # We default to a priority queue that returns the largest value
  block ||= lambda { |x, y| (x <=> y) == 1 }
  @heap = Containers::Heap.new(&block)
end

Public Instance methods

clear ()

Clears all the items in the queue.

[show source] 
# File lib/containers/priority_queue.rb, line 43
def clear
  @heap.clear
end
delete(priority) -> object
delete(priority) -> nil

Delete an object with specified priority from the queue. If there are duplicates, an arbitrary object with that priority is deleted and returned. Returns nil if there are no objects with the priority.

q = PriorityQueue.new
q.push("Alaska", 50)
q.push("Delaware", 30)
q.delete(50)            #=> "Alaska"
q.delete(10)            #=> nil
[show source] 
# File lib/containers/priority_queue.rb, line 109
def delete(priority)
  @heap.delete(priority)
end
empty? ()

Returns true if the queue is empty, false otherwise.

[show source] 
# File lib/containers/priority_queue.rb, line 48
def empty?
  @heap.empty?
end
has_priority? priority -> boolean

Return true if the priority is in the queue, false otherwise.

q = PriorityQueue.new
q.push("Alaska", 1)

q.has_priority?(1)    #=> true 
q.has_priority?(2)    #=> false
[show source] 
# File lib/containers/priority_queue.rb, line 62
def has_priority?(priority)
  @heap.has_key?(priority)
end
next -> object

Return the object with the next highest priority, but does not remove it

q = Containers::PriorityQueue.new
q.push("Alaska", 50)
q.push("Delaware", 30)
q.push("Georgia", 35)
q.next          #=> "Alaska"
[show source] 
# File lib/containers/priority_queue.rb, line 76
def next
  @heap.next
end
pop -> object

Return the object with the next highest priority and removes it from the queue

q = Containers::PriorityQueue.new
q.push("Alaska", 50)
q.push("Delaware", 30)
q.push("Georgia", 35)
q.pop         #=> "Alaska"
q.size        #=> 2
[show source] 
# File lib/containers/priority_queue.rb, line 91
def pop
  @heap.pop
end
push (object, priority)

Add an object to the queue with associated priority.

q = Containers::PriorityQueue.new
q.push("Alaska", 1)
q.pop #=> "Alaska"
[show source] 
# File lib/containers/priority_queue.rb, line 38
def push(object, priority)    
  @heap.push(priority, object)
end
size ()

Returns the number of elements in the queue.

q = Containers::PriorityQueue.new
q.size #=> 0
q.push("Alaska", 1)
q.size #=> 1
[show source] 
# File lib/containers/priority_queue.rb, line 28
def size
  @heap.size
end